Wireless communication systems are continually evolving and improving. However, there is a need for backward compatibility between new wireless communication systems that conform to a new standard and legacy wireless communication systems that conform to older standards. For example, Long Term Evolution, LTE, systems should be backward compatible with older systems such as Global System for Mobile Communication, GSM. In particular, it is desirable to provide short messaging services, SMS, via an LTE system, even though SMS is a technology based on circuit-switching, and LTE is a technology that is designed to support packet-switched services.
In current installations there is no support for direct communication between an SMS service layer, which receives, stores, and forwards SMS messages and a mobile management entity, MME, of an LTE network. Also, there is no support for direct delivery of trigger messages from a machine type communication interworking function, MTC-IWF, to an MME. Currently, if an SMS message or trigger message is to be sent to a user equipment, UE, it is first sent to a Mobile Switching Center, MSC. If the UE is not camped on the network served by the MSC, the MSC must send a failure message back to the SMS service layer or the MTC-IWF. The SMS service layer or MTC-IWF must then direct the SMS message or trigger message to a serving general packet radio service, GPRS, support node, SGSN. If the UE is not camped on the network served by the SGSN, then the SGSN sends a failure message back to the SMS service layer or MTC-IWF. In response to this second failure, the SMS service layer or the MTC-IWF will again send a message to the MSC, this time instructing it to forward the request to an MME serving an LTE network. This repetition of the process of seeking the UE may be time consuming, and also costly if the sending node (e.g. a gateway mobile switching center, GWMSC, or SMS router) and the MSC, SGSN, and MME are owned by different service operators.